A red tide bloom was one of the contributing factors to the third-deadliest year on record for manatees in Florida, according to a state report recently released.

The Florida Fish and Wildlife Conservation Commission says there were 538 overall deaths in 2017, which trails only 2013 (830) and 2010 (766).

"In terms of significant contributing factors around that area, besides boating, red tide definitely contributed to this higher number of mortalities in general in 2017," said Michelle Kerr, with FWC's manatee management program. "A red tide in the spring impacted manatees from Pinellas County to Collier."

"The manatees are effected through red tide by ingesting sea grass, where the toxin has built up, and through the air," Kerr said. "The primary route is through sea grass where the red tide algae has built up on the sea grass."

Katie Tripp, with Save the Manatee Club, said the red tide impact was noticeable but less than in past years, when hundreds of carcasses washed ashore.

"We had some red tide, and it was higher than last year, but some years you have hundreds die like you’ve seen in Lee County and Indian River Lagoon," Tripp said. "We didn’t see spikes like that."

Red tide is a harmful algal bloom because it releases a neurotoxin that causes fish, marine mammal and sea turtle kills while also causing respiratory issues in humans.

"Manatees suffering from red tide may lose the ability to remain upright and have difficulty breathing and lack of coordination," Kerr said.

Hundreds of people came out in the cold weather to watch manatees swim and play in the warm water at Manatee Park in east Fort Myers on Friday, January 5, 2017. (Photo: Amanda Inscore/The News-Press)

Lee was second in the state in overall deaths at 78, trailing Brevard County's total of 111.

Lee was No. 1 in the state for boat-related manatee deaths in 2017 for the seventh year in a row and the 10th time in the past 11 years.

Collier County had four boat-related kills and 11 overall recorded deaths, according to FWC records.

The number of boat deaths was 106, a number Tripp says can be lowered if all boaters paid attention while at the wheel.

"What I’m really focused on is trying to understand how many of those 106 were absolutely pure accidents where everybody was abiding by the law versus how many were hit when people just weren’t paying attention," Tripp said.

Biologists counted 6,620 manatees in February 2017, which is a baseline number and not an actual population estimate.

The counts are done during extremely cold conditions, when manatees are most likely to congregate in warm-water creeks and refuges like the Florida Power and Light plant along the Orange River just outside of Fort Myers.